In power systems, circuit breakers are used for connecting and disconnecting a load. During this process, the active elements of the circuit breaker either interrupt or incept high current, causing stresses in the circuit breaker as well as the connected power system components. The flow of the high current can be limited by closing and opening the circuit breaker at a specific instance on the source voltage waveform. A plurality of techniques are known for controlling the opening or closing of the circuit breaker in order to prevent generation of transient phenomenon. Such techniques rely on the usage of devices that perform synchronized switching control. One such device is the point on wave controller.
Point on wave controller is used for controlling switching instance of the circuit breaker. On receiving a command from a control unit, the point on wave controller advances the command to achieve closing or opening at an instance to minimize the current. The point on wave controller detects the opening or closing actuation time (also referred to as operating time) of the circuit breaker and calculates a time for switching in respect of the opening or closing command of the circuit breaker to ensure switching on a particular point on the voltage waveform. The point on wave controller determines the opening or closing actuation time as the time period between the instance at which the command was given to the circuit breaker and the instance at which electrical switching (i.e. interruption or inception of the electrical connection) happened.
Conventionally, for detecting the switching instance, the point on wave controller relies on current measurements from a current sensor connected to the load. However, for certain types of loads, such as inductive loads (transformers) or capacitive loads (transmission lines), the charging current is often of such small magnitudes that they cannot be accurately detected within the tolerance range of the current sensor and sensing accuracy required. Therefore, for such loads, current feedback based detection of switching instance cannot be applied.
There have been several attempts to solve the problem mentioned above. In one approach, instead of current, voltage has been used to determine the instance of switching. A voltage transformer is connected to the load. Based on the presence or absence of voltage, the point on wave controller determines the instance of switching. However, this voltage feedback approach is not applicable in scenarios where the load is already at a potential induced by electrostatic or electrodynamic means through a neighboring electrical element.
Therefore, in light of the abovementioned discussion, there is a need for a method and system that satisfies the above mentioned problems.